Accessing the spin structure of the orbital ES has been an experimental challenge, partly because of the short lifetime. For the \( V_B^- \)  color center, the excited state lifetime is only 1.2 ns at room temperature [1]}, [2]}. The photoluminescence spectrum of \( V_B^- \)  is a broad band emission at 4K, centered at \( \approx \)  850 nm, which makes it difficult to study the energy level structure of the ES by resonant excitation [3]}, [2]}, [5]}. In contrast, we present a simple approach that directly probes the ES spin transitions by using optically detected magnetic resonance (ODMR) technique at room temperature[6]}, [7]}. Through this technique, we obtained the detailed ES spin level structure including the hyperfine interaction to the surrounding nuclear spin, demonstrated controlled spin level mixing by means of magnetic field alignment, and showed the resulted tuning of optical illumination and ODMR contrast. These results deep our understanding of \( V_B^- \)  color center and help for the next step of developing \( V_B^- \)  color center spin as a solid-state quantum sensor.
